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There is limited information regarding the cause for the different etiologies in individuals with initial lateral ankle sprains (LAS) who have chronic ankle instability (CAI) and no recurrence or instability for 12 months (copers) following initial LAS. Assessing the movement patterns of copers and individuals with CAI and LAS recurrence is essential for identifying the mechanical factors that affect patient outcomes.Does coordination and coordination variability of rearfoot, midfoot, and forefoot present a potentially causative pattern for CAI or coper?This cross-sectional study included 35 males who were divided into the CAI (n = 13), coper (n = 12), and control group (n = 10). Participants performed rearfoot strike running on the treadmill at a fixed speed of 3.5 m/s. The coupling angle between the rearfoot, midfoot, and forefoot, representing intersegmental coordination, was calculated using the modified vector coding technique and categorized into four coordination patterns. The coupling angle standard deviation served represented coordination variability during the stance phase.One control participant and one CAI participant were excluded, and final analyses were performed on the CAI (n = 12), coper (n = 12), and control (n = 9) groups. During late stance, the coper group showed a significantly greater proportion of in-phase with distal dominancy (p = 0.02, effect size=0.17) and a significantly lower proportion of in-phase with proximal dominancy (p = 0.05, effect size=0.17), than the CAI group. During the early stance, the coper group showed a significantly lower proportion of anti-phase with distal dominancy than the CAI group (p = 0.03, effect size=0.18). There were no differences in intra-foot variability among the groups.The intra-foot coordination observed in the coper group suggests that this movement pattern may reduce the risk of ankle sprains.

In this study, the inferior fascicle of the anterior inferior tibiofibular ligament (AITFL) was classified to provide basic information to help elucidate the mechanism of ankle joint anterolateral impingement, and the morphological features of each type were compared for the purpose of clarification. This investigation examined 100 feet from 52 cadavers. The AITFL was classified into four types according to the presence or absence of the inferior fascicle and the positional relationship between the AITFL and the inferior fascicle of the AITFL. The morphological features of the AITFL that were measured included the fibre bundle length, fibre bundle width, fibre bundle angle, and the distance between the joint levels. A distinct, independent inferior fascicle of the AITFL was identified in 15 feet (15%). There were no significant differences in the morphological features based on differences in the AITFL classification. Therefore, these findings suggest that the presence or absence of the inferior fascicle and the difference in the positional relationship between the AITFL and the inferior fascicle of the AITFL are less likely to be involved in impingement during ankle dorsiflexion.

The purpose of this study was to investigate the strain applied to each of the tendon fiber bundles of the medial head of the gastrocnemius (MG), the lateral head of the gastrocnemius (LG), and the soleus muscle (Sol) that compose the Achilles tendon (AT) when the subtalar joint is pronated and supinated. Three AT twist types (least, moderate, extreme) were investigated. Using the MicroScribe system, the AT and the talocrural and subtalar joints were digitized to reconstruct three-dimensional models. Using this system, subtalar joint rotations in the pronation (20°) and supination (20°) directions were simulated, and the degrees of strain (%) on each tendon were calculated. For all twist types, when the subtalar joint was pronated, MG, LG, and Sol stretched, and when supinated, MG, LG, and Sol shortened. In particular, the least and severe twist types had large degrees of strain of Sol when the subtalar joint was pronated, and furthermore, each tendon fiber composing Sol had different degrees of strain. The study results suggest that the degree of strain applied within the AT with subtalar joint pronation is not constant, and that, especially in least and extreme twist types, the risk of developing AT disorders may increase.

Damage to the bifurcate ligament is one of the most difficult injuries to diagnose from imaging techniques. A probable reason for this is that the morphological characteristics of this structure have yet to be sufficiently elucidated. We, therefore, endeavored to elucidate the morphological characteristics of the bifurcate ligament through a large-scale study involving numerous specimens. This study included 100 feet from 52 formalin-fixed cadavers. The bifurcate ligament was classified into three types: presence of both calcaneonavicular ligament and calcaneocuboid ligament (Type I); absence of calcaneocuboid ligament (Type II); and absence of calcaneonavicular ligament (Type III). Morphological characteristics of the bifurcate ligament were determined by measuring fiber bundle length, width, and thickness at the center of each ligament. This classification resulted in 68 Type I feet (68%), 32 Type II feet (32%), and 0 Type III feet (0%). The calcaneonavicular ligament was 20.8 ± 2.9 mm long, 4.9 ± 1.2 mm wide, and 3.8 ± 1.1 mm thick. The calcaneocuboid ligament was approximately 10.5 ± 2.7 mm long, 4.7 ± 2.4 mm wide, and 1.5 ± 0.6 mm thick. The bifurcate ligament was located deep under the extensor hallucis brevis and extensor digitorum brevis muscles in all specimens. The calcaneal origin of the calcaneonavicular ligament was situated deep under the interosseous talocalcaneal ligament in all specimens. Two sides were identified in which the calcaneocuboid ligament was located deep under the dorsal calcaneocuboid ligament. Such variations and positional relationships were suggested to be factors complicating the diagnostic imaging of bifurcate ligament injuries. The present study results will likely form useful basic data for diagnostic imaging.

Background Medial tibial stress syndrome (MTSS) is one of the most common causes of exercise-related leg pain in runners. Because stopping training due to pain from MTSS could decrease the athlete’s competitiveness, it is necessary to construct MTSS prevention and treatment programs. However, the effect of running, which is believed to cause MTSS, on shear elastic modulus of the posterior lower leg is unclear. Therefore, the purpose of this study was to investigate the effect of 30 min of running on shear elastic modulus of the posterior lower leg in healthy subjects. Methods Twenty healthy males volunteered to participate in this study (age, 20.9 ± 0.6 y; height, 169.6 ± 4.5 cm; weight, 62.6 ± 5.2 kg). The shear elastic modulus of the posterior lower leg was measured using ultrasonic shear wave elastography before and immediately after a 30-min running task. Results Shear elastic moduli of the flexor digitorum longus and tibialis posterior were significantly increased after 30 min running task. However, there were no significant changes in shear elastic moduli of the lateral gastrocnemius, medial gastrocnemius, peroneus longus and peroneus brevis. Conclusion The results suggested that the increases in shear elastic moduli of flexor digitorum longus and tibialis posterior after running could be a risk factor for running-related MTSS development.

In this study, detailed investigations into the shape of the inferior patellar pole, the site of the patellar tendon attachment, and the length and course of the patellar tendon were performed with the aim of examining the anatomical factors involved in the developmental mechanism of patellar tendinitis. The investigation examined 100 legs from 50 cadavers. The inferior patellar pole was classified into three types: pointed, intermediate, and blunt. The attachment of the patellar tendon to the inferior patellar pole was classified into two types: an anterior and a posterior. The length of the patellar tendon was measured from the tibial tuberosity to the inferior patellar pole. The pointed type was seen in 57% of legs, the intermediate type in 21%, and the blunt type in 22%. Twenty-one legs were the pointed type, as well as the anterior type. The patellar tendon was significantly shorter with the posterior type than with the anterior type. The blunt type also had a significantly shorter patellar tendon than the pointed type. In legs that were both the pointed type and the anterior type, the inferior patellar pole and the proximal posterior surface of the patellar tendon impinged during knee flexion due to the posterior tilt of the patella, suggesting the possibility that this may induce damage. With the posterior type and blunt type, on the other hand, the possibility of strong tensile stress on the tendon fibers of the posterior facet of the inferior patellar pole was suggested.

Background Chronic ankle instability (CAI) may result from repeated, frequent ankle sprains during sports activities. Manual examination for CAI is conducted; however, quantitative methods for the evaluation of CAI have not been established, and the reproducibility of the amount of stress is low. This cross-sectional study aimed to use a stress device and ultrasound for the quantitative evaluation of the change in the length of the anterior talofibular ligament (ATFL) during simulated anterior drawer and ankle inversion stress tests. Methods Questionnaires were provided to 160 healthy college students (86 men, 74 women; 320 ankles). We extracted two groups from them: control subjects without a history of ankle injury (n = 64 ankles) and subjects with CAI (n = 54 ankles). We calculated the change in the length of the ATFL with anterior drawer and inversion stress tests at ankle joint plantar flexions of 0°, 20°, and 45° using ultrasound images. Results The anterior length change rates were significantly higher in the CAI group than in the control group at ankle joint plantar flexions of 20° and 45° in men (P

The aim was to clarify the relationships between differences in the number of fiber bundles of the anterior talofibular ligament (ATFL) and differences in the angle of the calcaneofibular ligament (CFL) with respect to the long axis of the fibula and their effects on ankle braking function. The study sample included 110 Japanese cadavers. ATFLs were categorized as: Type I with one fiber bundle; Type II with two fiber bundles with incomplete separation and complete separation; and Type III with three fiber bundles. The CFLs were categorized according to the angles of the CFLs with respect to the long axis of the fibula and the number of fiber bundles. Six categories were established: CFL10° (angle of the CFL with respect to the long axis of the fibula from 10° to 19°); CFL20° (range 20°–29°); CFL30° (range 30°–39°); CFL40° (range 40°–49°); CFL50° (range 50°–59°); and CFL2 (CFLs with two crossing fiber bundles). ATFL was Type I in 34 legs (31%), Type II in 66 legs (60%), and Type III in 10 legs (9%). Five CFL categories were identified: CFL10° in 4 feet (3.7%); CFL20° in 23 feet (20.9%); CFL30° in 34 feet (30.9%); CFL40° in 33 feet (30%); CFL50° in 15 feet (13.6%); and CFL2 in one foot (0.9%). Type III contained mainly CFL40° and CFL50° (7 of 10 feet). ATFL and CFL appear to cooperate in the ankle joint braking function.

The purpose of this research was to clarify the relationships between quadratus plantae (QP) and flexor digitorum longus (FDL) and flexor hallucis longus (FHL) using large-scale specimens. This study examined 116 legs from 62 Japanese cadavers. The QP was classified as: Type I, formed by the lateral and medial heads; Type II, the lateral head is absent; and Type III, the medial head is absent. The FHL branches to the lesser toes were classified as: Type A, connection from FHL to toe 2; Type B, connection from FHL to toes 2 and 3; Type C, connection from FHL to toes 2–4. Next, the relationships between QP and FHL and FDL were observed. Type I accounted for 87%, Type II for 10%, and Type III for 3%. Type A accounted for 33%, Type B for 53%, and Type C for 14%. Regarding the relationship between QP and FDL, regardless of the classification of the connections of the FHL tendon slip to the lesser toes, QP attachments to FDL branching to toes 2, 3, and 4 were seen in 47–59%. Furthermore, QP attachments to FDL branching to toes 2, 3, 4, and 5 were seen in 41–47%. QP appears to function strongly to counter the oblique pull of FDL and FHL and as a lesser digit plantar flexor.

The spinal reciprocal inhibition during co-contraction remains unclear. Reports on the reciprocal Ia and D1 inhibitions in the co-contraction are lacking, and a point about the muscle activity amount during co-contraction is unclear. This study aimed to clarify the influence of changes in the ratio of soleus (Sol) and tibialis anterior (TA) muscle activities in co-contraction on reciprocal Ia and D1 inhibitions. Twenty healthy adults were subjected to four stimulatory conditions: a conditioning stimulus–test stimulation interval (CTI) of − 2, 2, or 20 ms or a test stimulus without a conditioning stimulus (single). Co-contraction [change in (Sol)/(TA) activity] was examined at task A, 0%/0% maximal voluntary contraction (MVC); task B, 5%/5% MVC; task C, 15%/15% MVC; task D, 5%/15% MVC; and task E, 15%/5% MVC. At 2-ms CTI, the H-reflex amplitude value was significantly lower in tasks A, B, C, and D than in the single condition. Among the tasks, the H-reflex amplitude values were lower for A, B, C, and D than for E. At 20-ms CTI, the H-reflex amplitude was significantly lower in tasks A, B, C, D, and E. Among the tasks, the H-reflex amplitude was significantly lower from task A and B to task E. The change in the muscle activity ratio during co-contraction could modulate reciprocal Ia inhibition depending on the Sol/TA muscle activity ratio. D1 inhibition at rest did not differ significantly when the Sol/TA ratio was equal or when TA muscle activity was high. During co-contraction with high Sol muscle activity, D1 inhibition decreased from rest.

Introduction The medial tibial stress syndrome is one of the most common causes of running-related injuries. The primary study objective was to observe the attachment proportion of flexor digitorum longus and soleus, at the most common location of medial tibial stress syndrome, using ultrasonography, on a large cohort of young males and females to evaluate for gender-based anatomical differences. The secondary objective of this study was to investigate the relationship between the anatomical features and medial tibial stress syndrome. Methods In this study, we observed whether or not flexor digitorum longus and/or soleus attached at the middle and distal thirds of the medial margin of the tibia (most common location of medial tibial stress syndrome) using ultrasonography. History of medial tibial stress syndrome was defined by inquiries. Results The Chi2 tests showed that the attachment proportion of the soleus in female participants was significantly higher than that observed in male participants. In addition, Chi2 testing showed that there were no significant differences between attachment proportion of soleus of legs with history of medial tibial stress syndrome and legs without history of medial tibial stress syndrome, in both male and female participants. Conclusions These results suggested that the anatomical features of flexor digitorum longus might be involved in medial tibial stress syndrome development, whereas the anatomical features of the soleus might not be involved in medial tibial stress syndrome development. Level of evidence III, cross-sectional study.

The aim was to clarify the effect of differences in the number of fiber bundles of the anterior tibial ligament (ATFL) on ankle braking function. The study sample included 81Japanese cadavers. ATFLs were categorized as: Type I with one fiber bundle; Type II with two fiber bundles that were completely separated; and Type III with three fiber bundles. Three-dimensional reconstructions of a single specimen from each category were then created. These were used to simulate and calculate ATFL strain during dorsiflexion (20°) and plantarflexion (30°) on the talocrural joint axis and inversion (20°) on the subtalar joint axis. Almost all types of superior fiber lines were stretched with dorsiflexion and plantarflexion. Regardless of Type, the inferior fiber line was shortened with plantarflexion and stretched with dorsiflexion. The inferior fiber bundle of Type III was shortened only at plantarflexion 30° and inversion 20°, but in all others it was stretched. The results suggest that Type III was weaker than Type I and Type II in terms of ankle plantarflexion and inversion braking function.

The aims of this study have been to clarify differences in morphological features based on the number of fiber bundles in the anterior talofibular ligament (ATFL), and to investigate the relationship between the ATFL and the calcaneofibular ligament (CFL). This study used 81 legs from 43 cadavers. The ATFL was classified according to differences in the number of fiber bundles as: Type I, with one fiber bundle; Type II-a, with two fiber bundles that were incompletely separated; Type II-b, with two fiber bundles that were completely separated; and Type III, with three fiber bundles. The morphological features measured were fiber bundle length, fiber bundle width, and fiber bundle angle. For the relationship between the ATFL and CFL, the positional relationship and attachment sites of the two ligaments were examined. Type I was present in 33%, Type II-a in 17%, Type II-b in 40%, and Type III in 10%. The morphological features of superior fiber bundles and inferior fiber bundles were significantly different within each type. Among types, there were significant differences in the morphological features of Type II-a and Type III inferior fiber bundles. In the relationship between the ATFL and CFL, there was a connection between the ATFL and CFL in all specimens. Various types were present in the positional relationship and attachment sites of the two ligaments. The results of this study suggest that, among different ligament types with two or three fiber bundles, the control function of the ankle may differ within each type and among types.